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The use of biodiesel in conventional diesel engines results in increased NOx emissions; this presents a barrier to the widespread use of biodiesel. The origins of this phenomenon were investigated using the CFD KIVA3V code, which was modified to account for the physical properties of biodiesel and to incorporate semi-detailed mechanisms for its combustion and the formation of emissions. Parametric φ-T maps and 3D engine simulations were used to assess the impact of using oxygen-containing fuels on the rate of NO formation. It was found that using oxygen-containing fuels allows more O₂ molecules to present in the engine cylinder during the combustion of biodiesel, and this may be the cause of the observed increase in NO emissions.

Biodiesel blends are promising alternatives to diesel fuel, but, reduced quantitative information is available on the impact of biodiesel on engine systems behaviour, durability and economical aspects in fleet cost management. A representative sample of urban buses fuelled with B50 was compared with the same type of vehicle fuelled with conventional petroleum fuel. The objective was to assess the effects of B50 upon important parameters such as: fuel consumption, power loss and drivability; the effects on the fuel system and engine oil and the implications regarding the maintenance programme. These implications could be very relevant upon a fleet manager's decision to select biodiesel as an alternative fuel. The results obtained show that there was no difference in the serviceability of the buses fuelled with B50 compared with those fuelled with petroleum diesel fuel, and additionally, no change in the maintenance programme was required for this type of B50 fuel.